Fuel control system for gas turbine engines, particularly engines utilizing afterburning



iinited States Patent FUEL CONTROL SYSTEM FOR GAS TURBINEEN- GINES, PARTICULARLY ENGINES UTILIZING AFTERBURNING `Elmer A. Haase and Charles S. 'Longstreeh South Bend,

Ind., assignors to The Bendix Corporation, a corporation of Delaware Filed July 28, 1952, Ser. No. 301,286

5 Claims. (Cl. 60-39.28)

In prior applications Serial No. 167,638,1iled June l0, 1950, now Patent No. 2,778,312, in the names of Ward C. Suttle and Elmer A. Haase, and Serial No. 225,407, filed May 9, 1951, in the name of Elmer A. Haase, both of which have been assigned to the assignee of the instant invention, there are disclosed fuel control systems for regulating the supply of afterburning fuel to a gas turbine engine employing a centrifugal fuel pump driven by an air turbine receiving its air supply from the engine compressor across a pressure-sensitive poppet valve which in the first instance is controlled as a function of pump discharge pressure and in the second instance as a function of the drop or differential across the said valve. In Serial No. 167,638 the apparatus functions to limit pump outlet pressure to a predetermined maximum value, while in Serial No. 225,407 pump delivery pressure is scheduled in accordance with variations in compressor discharge Pressure.

The ultimate aim in both the two preceding applications and the instant application is to provide afterburning fuel control apparatus which maybe embodied in a compact, relatively light package and which at the same time will meter fuel at the most efficientrate with a minimum drain on the compressor.

The present invention utilizes an air turbine-driven fuel pump and associated controi mechanism-having certain features in common with the apparatus of the above-noted prior applications. An important difference, however, is that means are provided for metering -fuel to the afterburner nozzles as a function of the rise across the compressor. The main poppet valve which controls the admission of compressor bleed-off pressure to the turbine nozzle chamber is in turn controlled by a servo-valve responsive to compressor rise andthe drop or differential across a metering jet in the fuel conduitbetween `the fuel pump and afterburner fuel nozzles. The servo valve thus controlled operates to position the puppet valve in a manner such as to admit .sufficienti pressure to the turbine to cause the latter to drive thefuel pump at a rate which ensures the required fuel fiows and pressures while at the same time thecontrollisstable under all conditions of operation.

The primary object of the present invention therefore is to provide an improved control for metering fuel to the burner system of a gas turbine engine, and particularly to the afterburning system therefor, which is efficient in operation and stable under all conditions of operation.

Another object is to improve the metering characteristics and render more stable apparatus such as that disclosed in the foregoing copending applications.

These and other objects will become apparent in View of the following description taken in conjunction with the drawings, wherein the single figure illustrates in sectional schematic a gas turbine engine vand associated fuel control apparatus in accordance with the invention.

Referring to the drawing in detail, a turbo jet engine is generally indicated at it has the usual burner system 11, to which fuel may be supplied in any convenice ient manner from Ya suitable source of supply by way of a main control fuel device 12, manifold 12' Vand nozzles 13, the liquid fuel being mixed with air supplied under pressure by compressor 14 and the expanded air and products of combustion acting on the blades of a turbine 15 to effect rotation of the latter, which in turn drives the compressor. The exhaust gases then pass into tail pipe chamber 16, defined by tail pipe l17, and out through exhaust jet 18 to effect propulsion of theaircraft in which thek engine may be mounted.

The effective area of the exhaust jet 18 may be varied by a so-called bullet valve 19, actuated by a servo motor 20, which in this instance is of the-air pressure type and comprises `a servo piston 21 and power cylinder 21. Air under pressure is communicated by way of pipe line 22 and branch line 22 to a servo valve cylinder 423, having therein-a valve24, actuated to bullet-retracting position by `a solenoid 25. As long as solenoid 25 remains unenergized, valve 24 will remain in its up position, at which time air under pressure is communicated by way of pipe lines 22 and 26 to the left-hand side of servo piston 21, moving bullet valve 19 to a position for maximum jet thrust under normal conditions of operation. When the solenoid 25 is energized, the valve 24 moves downwardly and air under pressure is admitted to theright-hand side of the servo piston 21 by way of pipelines 22, 22 and 27, whereupon the bullet valve 19 is retracted to a Vposition for maximum jet area, which is the afterburning position. The solenoid 25 is energized automatically by means of an electronic amplifier 28, adapted to respond to changes in temperature above and below a predetermined set temperature as sensed by a pair of thermocouple elements 29and30, located at spaced points in the tail pipe chamber 16. When a temperature above a certain predetermined value obtains in said chamber, the amplifier closes a-circuit to the solenoid 25 through wires 31 and 32, thereby causing the valve 24 to move downwardly, whereupon air under pressure flows-to the right-hand side of servo piston 21 and the bullet valve 19 is retracted as above noted.

The afterburning fuel may be ignited by means of a spark plug or similar device indicated at 33 and supplied with current by way of an electrical circuit indicated at 34 and 35.

The afterburning fuel control apparatus, which incorporates the present invention, comprises a centrifugal pump 36, which is fixed on Aa shaft '37, rotatably supported by bearings 38 and 38'. A'n air turbine 39, provided with blades 39, is fixed on the opposite or'lefthand end of shaft 37 and functions to Vdrive the pump V'35. The pump and turbine assembly is located in a housing 40, defining a fuel conduit 41, having a metering restriction 12,2 therein, the saidconduit discharging into a fuel manifold 43, from which the afterburning fuel flows to a purality of discharge nozzles 44, arranged to "spray afterburner fuel into the tail pipe chamber 16. A cutoff valve 45, here shown .as of the normally closed type 4actuated to open position by .an electrical solenoid 45',

is provided for shutting off fiow to the afterburner nozzles and preventing nozzle drip. Y

The solenoid 45' and amplifier 28 are connected into an electrical circuit including wires 46, 46 and 47, '47', receiving current from a suitable source of supply. A switch 48 controls energization of the main circuit'and may be located within convenient reach of a pilot or operator.

Air underrpressure for driving the turbine 39 is taken off from any 'desired stage of the compressor 14 by way of a conduit a9 and is delivered to an inlet pressure chamber 59, from which it Vflows to a nozzle chamber 51 across an orice 52, 'controlled by a poppet `valve 53, the latter being mounted on the movable end of a bellows 54, defining an expansible chamber 54'. When the valve 53 opens, air under pressure may flow from inlet chamber 50 to nozzle Yclimaber 51 and thence through nozzle orice 55 to effect rotation of the turbine 39, the exhaust air flowing out through passage 56.

The pressure interiorly of the bellows 54, or in the expansible chamber 54', is variable as a function of the rise across the compressor 14; it is communicated thereto by way of a conduit 57, having its inlet end exposed to compressor outlet or P2 pressure, said conduit 57 communicating with an extension 57 thereof across an orifice 58, controlled by a valve 59, the latter being resiliently connected to a servo piston 60 by means of a spring 61, which at one end engages a collar or flange 62, formed on the inner end of the valve stem, and its opposite end a similar collar or flange 63, formed interiorly of the piston 60. The piston 60 is mounted in a chamber 64, defining a power cylinder. At the lefthand side of piston 6i), the power cylinder or chamber 64 communicates with compressor discharge pressure by way of passage 65 and conduit 57, and at its opposite or right-hand side communicates with compressor inlet pressure by way of passage 66 and conduit 67.

1t will be seen that the piston 60 is subjected at opposite sides to compressor inlet pressure and compressor discharge pressure and hence will respond to the rise across the compressor and will be positioned as a function of compressor rise. Movement of the piston repositions the valve 59 and hence determines the area of the orifice 58 controlled by the valve 59 and the degree of pressure in expansible chamber 54.

The piston 60 is connected to a diaphragm 68 by means of a slide rod 69, the said diaphragm being exposed to the fuel differential across the metering jet 42. To this end, a passage 70, having a restriction 71 therein, communicates pressure upstream of the jet 42 to a chamber 72 on the right-hand side of the diaphragm, while pressure downstream of said jet is communicated to chamber 73 on the left-hand side of said diaphragm by way of passage 74, having a restriction 75 therein. A selectively variable dash-pot action of the diaphragm 68 and parts connected thereto including control valve 59 is had by means of a passage 76, which communicates chambers 72 and 73 across a restriction 77 of predetermined iowY capacity. This dashpot action tends to stabilize the system.

To further stabilize and reduce the tendency of the system to hunt, a certain degree of pressure in the nozzle chamber 51 is communicated to the expansible bellows chamber 54', by way of passage 78, restriction 79, valve chamber 80, orifice 81 and passage 82. The action resulting from the stabilizing bleed 79 will be more fully set forth in the description of operation.

Orifice 81 is controlled by a quick starting and stopping valve 83, actuated by a solenoid 84, which is connected into the main electrical circuit by wires 85 and S6.

Operation During normal engine operation (without afterburning), the parts will be in the respective positions shown in the drawings. Thus, the bullet valve 19 will be in its forward or normal area position, the switch 48 will be open, the main afterburning circuit 46, 46', 47 and 47 unenergized and the fuel cut-off valve 45 and the startand-stop valve 83 will be closed. Since the fuel differential across restriction 42 will be zero, control valve S9 will be closed and air will be locked in expansible chamber 54', holding valve 53 closed.

Assuming now that the pilot desires to go into afterburning, he will close switch 48, whereupon the ignition circuit 34, 35 will be energized, valves 45 and 83 will be retracted, and the amplifier 2S will be energized or conditioned to respond to an increase in temperature in the tail pipe chamber 16. Since a high compressor pressure is present in chamber 50, the valve 53 will immediately -expansible bellows chamber 54.

open and pressure will build-up in the nozzle chamber 51 and start rotation of the turbine 39 and hence the centrifugal fuel pump 36. This starts fuel flowing in conduit 41 across the metering restriction 42; however, the diaphragm 68 immediately senses the differential across the said restriction and tends to open the control valve 59, but opening of the latter is opposed by the compressor PZ-Pl differential which is imposed across the piston 60, tending to close the Valve. The valve 59 is thus positioned by the net force of the differential across the air piston and the fuel head or differential across the fuel diaphragm. At any given PZ-Pl differential, these forces are in balance and the metering head established by the centrifugal pump 36 will be proportional to the pressure rise across the compressor. Since the pressure rise across the compressor, which varies generally as the square of the airflow therethrough, is balanced against the fuel head across metering restriction 42, which varies as the square of the fuel flow therethrough, it is apparent that a substantially constant fuel-to-air ratio will be established in the afterburner section of the tailpipe when the afterburner is in use, irrespective of variations in altitude. Results have shown that metering, calibrated as a function of compressor rise provides the required amount of afterburning fuel for maximum thrust efciency without waste and with a minimum of bleed-off from the compressor.

As soon as afterburning fuel in the tail pipe chamber ignites and the temperature therein rises to a predetermined value, the solenoid 25 moves downwardly, air under pressure is communicated to the right-hand side of servo piston 21 and the bullet valve 19 is retracted. Afterburning now proceeds until the switch 48 is opened, whereupon the parts resume their respective positions for normal engine operation.

The tendency of the system to hunt is materially reduced by bleeding nozzle chamber 'pressure into the This is due to the fact that the nozzle chamber 51 senses the changes that Will take place at the metering jet 42 preceding such changes and tends to dampen rapid changes in position of the valve 53.

The particular arrangement of the fuel control valve 59 and its associated parts permits easy change-over to metering as a function of parameters other than compressor rise. Thus by venting conduit 57 to compressor discharge pressure corrected for changes in atmosphere pressure, fuel ow could be made proportional to compressor discharge pressure absolute. Also by connecting the valve 59 to a mach meter, it could be controlled to permit ow of afterburning fuel only at aircraft speeds below a predetermined Value and flow then maintained substantially constant at a given aircraft speed. Instead of connecting the mach meter to valve 59, the same result could be accomplished by connecting the meter to a Valve adapted to vary the area of the metering jet 42.

Although only one embodiment of the invention has been schematically illustrated and described, certain changes in form and relative arrangement of parts may be made to adapt the invention for use with engines having different characteristics.

We claim:

1. For use n the fuel system of a gas turbine engine having an air compressor, a fuel conduit having a metering restriction therein, a centrifugal fuel pump for pressurizing fuel in said conduit across said restriction, an air turbine for driving said pump, a passage for communicating air under pressure from the compressor to said air turbine for driving the latter, a valve controlling the flow of air through said passage, means for positioning said valve as a function of compressor inlet to outlet pressure differential, and means for bleeding pressure from said passage to said last named means to dampen the action of said valve.

assenso 2. For use in the fuel system of a gas turbine engine having an air compressor, a fuel conduit having a fixed area metering restriction therein, a fuel pump for pressurizing fuel in said conduit across said restriction, said metering restriction being in flow controlling relationship with the entire output of said pump, an air turbine for driving said pump, a flow passage for communicating air under pressure from the compressor to said air turbine for driving the latter, a uid pressure responsive valve for regulating the ow of air through said passage, a pilot valve for controlling said Huid pressure to which said first named valve responds, first means operably connected to low and high fluid pressure source associated with said compressor and being responsive to the pressure differential between said pressure sources, second means responsive to a fuel pressure derived from said fuel conduit, said first and second means coacting with said pilot valve for controlling said pilot valve and a restricted passage for bleeding pressure from said ilow passage downstream from said uid pressure responsive valve to said iluid pressure responsive valve to dampen the action thereof.

3. For use in the fuel system of a gas turbine engine having an air compressor, a fuel conduit having a metering restriction therein, a fuel pump for pressurizing fuel in said conduit across said restriction, an air turbine for driving said pump, a ow passage for communicating air under pressure from said compressor to the air turbine for driving the latter, a valve for controlling ow of air through said passage, an expansible chamber partially defined by said valve and tending to urge the latter towards closed position, a passage for communicating a uid under pressure to said eXpansible chamber, a control valve for regulating the flow of fluid through said. latter passage, means responsive to a pressure derived from the compressor for controlling said control valve, and a restricted passage for bleeding pressure from said ilow passage downstream from said valve to said expansible chamber to dampen the action of said valve.

4. For use in the fuel system of a gas turbine engine having an air compressor, a fuel conduit having a metering restriction therein, a fuel pump for pressurizing fuel in said conduit across said restriction, an air turbine for driving said pump, a nozzle chamber upstream of said turbine, a passageway for communicating air under pressure from the compressor to said nozzle chamber, a valve for controlling ilow of air through said passageway, an eXpansible chamber for controlling the response of said Valve, a control valve for regulating a flow of air to said expansible chamber, and means for bleeding pressure from said nozzle chamber to said expansible chamber to dampen the action of said valve.

5. For use in a fuel system of a gas turbine' engine having an air compressor, a fuel conduit having a metering restriction therein, a fuel pump for pressurizing fuel in said conduit across said restriction, an air turbine for driving said pump, a flow passage for communicating air under pressure from said compressor to the air turbine for driving the latter, a valve for controlling ow of air through said passage, means defining an expansible chamber associated with said valve and tending to urge the latter towards closed position, a passage for communicating a liuid under pressure to said expansible chamber, a control valve for regulating the ow of fluid through said latter passage, means responsive to the rise across the compressor for controlling said control valve, and means for bleeding pressure from said ow passage downstream from said valve to said expansible chamber to dampen the action of said Valve.

References Cited in the file of this patent UNITED STATES PATENTS 2,503,048 Iiield Apr. 4, 1950 2,545,815 Klinge Mar. 20, 1951 2,550,678 Deacon May 1, 1951 2,555,445 Hooker et al. June 5, 1951 2,563,025 Goddard Aug. 7, 1951 2,565,854 Johnstone et al. Aug. 28, 1951 2,610,464 Knoll Sept. 16, 1952 2,643,514 Jubb June 30, 1953 2,706,888 Ballantyne et al Apr. 26, 1955 2,714,803 Abild Aug. 9, 1955 2,739,442 Neal et al. Mar. 27, 1956 2,742,755 Davies et al Apr. 24, 1956 UNITED STATES PATENT oEEICE CERTIFICATION OF CORRECTION December 27, 1960 Patent No. 2,9v,O3O

Elmer A, Haasev et al l ted that error appears in the above numbered pat- It s hereby oer d that the said Letters Patent should read as ent requiring correction an corrected below'.

Column 5, line 13, for "source" read sources Signed and sealed this 4th day .of July 1961.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents 

